rx.run on an empty observable confusingly errors with a CancelledError

[GregRos]

Example code:

import aioreactive as rx
async def start():
    empty = await rx.run(rx.empty())

We get the error:

Exception has occurred: CancelledError 
exception: no description
  File "/home/gr/.pyenv/versions/3.13.2/lib/python3.13/asyncio/tasks.py", line 507, in wait_for
    return await fut
...

If rx.run errors on an empty input, the error thrown should say so explicitly.